1. Field
The following description relates to a power semiconductor device and a fabrication method thereof and to, for example, an insulated gate bipolar mode transistor (IGBT) and a power semiconductor device with improved resistivity dispersion which is implemented with such an IGBT.
2. Description of Related Art
In recent years, due to the shortage of energy, researches on energy-saving mechanisms and energy-efficient products and on alternative energy development have been actively taking place worldwide. With such a movement, interests in smart grids, electric vehicles, and photovoltaic power generation are increasing. As a result, the importance of a power conversion apparatus as one of the most important parts in such a system is being recognized. As power conversion apparatuses that are in use increase in their capacity, the modern power conversion apparatuses have to keep up with the demand for high current and high voltage operations, while still maintaining low on-resistance and fast response speed for efficiency, as well as operating at a high frequency to allow the minimization in size and weight of the overall device.
IGBTs are considered a suitable power semiconductor device to meet these demands. A shallow low concentration drift region enables reduction in on-resistance loss, implementation of high-frequency products with adjustment of switching speed through concentration adjustment of a P type collector region and moving time control of minority carriers, and implementation of high-voltage endurance (for example, above 1200 V) and high current (for example, several hundreds of amperes) in application to a module.
FIG. 1 illustrates a cross-sectional view of an example of an IGBT.
As illustrated in FIG. 1, an IGBT may include a substrate 100, a P+ type region 110, an N+ type region 120, a gate electrode 130, an emitter electrode 140, a field stop layer 150, and a P+ type collector layer 160.
The high concentration field stop layer 150 reduces an electric field formed between the low concentration N− type substrate 100 and the P+ type collector layer 160 gradually to 0 (zero) before the electric field reaches the P+ type collector layer 160. FIG. 1 illustrates the changes in electric field along a depth of the IGBT. In the technology before using the field stop layer 150, a very thick substrate having a thickness of 200 μm were used to cause the electric field to be 0 (zero) in an off-state. Further, a doping concentration of the substrate has to be reduced to increase resistance. In this case, the doping concentration of the substrate is heavily changed to increase voltage overshoot, and the switching loss is relatively increased due to the thick substrate. Thus, a field stop layer 150 may be used to solve these issues. When the field stop layer 150 is used, a thick substrate is not necessary. The substrate may have a relatively thin thickness of approximately 120 μm.
For example, as a substrate 100, an N− type drift region that is a floating zone (FZ) wafer may be used. The high concentration field stop layer 150 is formed on a rear side of the FZ wafer. That is, the field stop layer 150 is formed in the FZ wafer, and the FZ wafer is fabricated by implanting ions into an edge portion of an intrinsic wafer and diffusing the implanted ions. Therefore, the concentration distribution of the doped dopant in the FZ wafer is not uniform; the concentration is higher at the edge portion of the FZ wafer, and than is gradually reduced toward a center of the FZ wafer. Because the dopant concentration changes substantially according to a location within the FZ wafer, the voltage overshoot in the IGBT may increase and a swing width in a collector-emitter voltage Vce,sat may change substantially.
In an IGBT having such a structure, because the dopant concentration changes substantially based on the location within the FZ wafer, resistivity distribution of the substrate 100 may increase to more than 10%; as a result, the switching speed of the field stop layer 150 and the swing width in the collector-emitter voltage Vce,sat may also increase.